1. Field of the Invention
The present invention relates to an illumination apparatus, an image sensor unit, and a paper sheet discriminating apparatus.
2. Description of the Related Art
A light-guide type illumination apparatus is known as an illumination apparatus used in an image sensor unit.
Japanese Laid-open Patent Publication No. 9-214675 discloses a light source unit (illumination apparatus) with LED lamps installed on both end faces of a light guide to obtain more light.
An LED module may be used as a light source of the illumination apparatus, the LED module including LED chips arranged on a light emitting surface of a plate-like supporting body, the LED chips sealed by a transparent resin. In some LED modules, the LED chips are deviated and arranged closer to one side in a width direction relative to a center position of the light emitting surface in the width direction. When the LED modules with the deviated LED chips are set on both end faces of a light guide, there is a problem that the illumination apparatus is enlarged and that the image sensor unit is enlarged accordingly.
LED chips with red, green, blue, as well as infrared and ultraviolet emission wavelengths for example may be used in light sources of an illumination apparatus applied to a paper sheet distinguishing apparatus that authenticates paper sheets, such as bills and securities, in order to read invisible ink for the security. Therefore, the number of lead terminals of the LED module increases, and the LED module is enlarged. As a result, there is a problem that the illumination apparatus and the image sensor unit are further enlarged.
Light sources in different shapes can also be used as LED chips set on both ends of a light guide as in Japanese Laid-open Patent Publication No. 2007-299775. However, if the LED chips in different shapes are used, the cost is greater than when LED chips in the same shape are used at both ends.
FIG. 14 is a perspective view illustrating an arrangement of an illumination apparatus 100 according to a comparative example. The illumination apparatus 100 includes a light guide 101, a first LED module 104, a second LED module 106, and a circuit board 108. The light guide 101 causes light from the first LED module 104 to enter from one of both end faces in a longitudinal direction and causes light from the second LED module 106 to enter from the other end face. The light guide 101 causes a diffusing surface 103 to reflect and diffuse the light entered from both end faces to thereby emit the light to an original from a light emission surface 102.
The first LED module 104 and the second LED module 106 have the same outer shape and structure, have a dimension W in the width direction, and are mounted on the circuit board 108. The first LED module 104 includes an LED chip 105 closer to one side relative to the center position in the width direction, and the second LED module 106 includes an LED chip 107 closer to the same one side relative to the center position in the width direction. Therefore, if the LED chip 105 of the first LED module 104 and the LED chip 107 of the second LED module 106 are mounted on the circuit board 108 facing each other across the light guide 101, the dimension is enlarged in the width direction (sub-scan direction) when viewed in an arrow G direction (main-scan direction).
FIG. 15 is a view from the arrow G direction of FIG. 14. As illustrated in FIG. 15, protrusion lengths of the first LED module 104 and the second LED module 106 in the width direction are long when viewed from the arrow G, because an overlap margin of the two in the width direction is small. Therefore, a dimension T1 of a combination of the first LED module 104 and the second LED module 106 in the width direction is enlarged. In this case, the dimension of the circuit board 108 to be provided with the first LED module 104 and the second LED module 106 also needs to be large in the width direction, and the illumination apparatus 100 is enlarged. This leads to an enlargement of the image sensor unit using the illumination apparatus 100.